Barack Obama speaks to jubilant crowds at his victory rally in Chicago
Democratic Senator Barack Obama has been elected the first black president of the United States, prompting celebrations across the country.
"It's been a long time coming, but tonight... change has come to America," the president-elect told a jubilant crowd at a victory rally in Chicago.
His rival John McCain accepted defeat, and called on his supporters to lend the next president their goodwill.
The BBC's Justin Webb says the result will have a profound impact on the US.
He says the American people have made two fundamental statements about themselves: that they are profoundly unhappy with the status quo, and that they are slamming the door on the country's racial past.
McCain: 'We must work together'
Mr Obama appeared with his family, and his running mate Joe Biden, before a crowd of tens of thousands in Grant Park, Chicago.
Many people in the vast crowd, which stretched back far into the Chicago night, wept as Mr Obama spoke.
"If there is anyone out there who still doubts that America is a place where all things are possible, who still wonders if the dream of our founders is alive in our time, who still questions the power of our democracy, tonight is your answer," he said.
He said he had received an "extraordinarily gracious" call from Mr McCain.
He praised the former Vietnam prisoner-of-war as a "brave and selfless leader".
"He has endured sacrifices for America that most of us cannot begin to imagine," the victor said.
He had warm words for his family, announcing to his daughters: "Sasha and Malia, I love you both more than you can imagine, and you have earned the new puppy that's coming with us to the White House."
But he added: "Even as we celebrate tonight, we know the challenges that tomorrow will bring are the greatest of our lifetime - two wars, a planet in peril, the worst financial crisis in a century.
"The road ahead will be long. Our climb will be steep. But America - I have never been more hopeful than I am tonight that we will get there."
Hours after Mr Obama's victory was announced, crowds were still celebrating on the streets of Washington DC and Mr Obama's hometown of Chicago.
From red to blue
Mr Obama captured the key battleground states of Pennsylvania and Ohio, before breaking through the winning threshold of 270 electoral college votes at 0400 GMT, when projections showed he had also taken California and a slew of other states.
Obama tells his supporters: "Change has come to America."
Then came the news that he had also seized Florida, Virginia and Colorado - all of which voted Republican in 2004 - turning swathes of the map from red to blue.
Projected results have yet to be announced for the states of North Carolina and Missouri, which are believed to be too close to call.
However, at 1100 GMT, Mr Obama's share of the popular vote stood at 52.3%, compared with Mr McCain's 46.4%.
The main developments include:
Mr Obama is projected to have seized Ohio, New Mexico, Iowa, Virginia, Florida, Colorado, Indiana and Nevada - all Republican wins in 2004.
He is also projected to have won: Vermont, New Hampshire, Pennsylvania, Illinois, Delaware, Massachusetts, District of Columbia, Maryland, Connecticut, Maine, New Jersey, Michigan, Minnesota, Wisconsin, New York, Rhode Island, California, Hawaii, Washington, Oregon.
Mr McCain is projected to have won: Montana, Alaska, Kentucky, South Carolina, Oklahoma, Tennessee, Arkansas, Alabama, Kansas, North Dakota, Wyoming, Georgia, Louisiana, West Virginia, Texas, Mississippi, Utah, Arizona, Idaho, South Dakota.
Turnout was reported to be extremely high - in some places "unprecedented".
The Democrats increased their Senate majority by five seats, but fell short of the 60 needed to stop blocking tactics by Republicans. They also increased their majority in the House of Representatives.
Exit polls suggest the economy was the major deciding factor for six out of 10 voters.
Nine out of 10 said the candidates' race was not important to their vote, the Associated Press reported. Almost as many said age did not matter.
Several states reported very high turnout. It was predicted 130 million Americans, or more, would vote - more than for any election since 1960.
Many people said they felt they had voted in a historic election - and for many African-Americans the moment was especially poignant.
John Lewis, an activist in the civil rights era who was left beaten on an Alabama bridge 40 years ago, told Atlanta's Ebenezer Baptist Church: "This is a great night. It is an unbelievable night. It is a night of thanksgiving."
Besides winning the presidency, the Democrats tightened their grip on Congress.
The entire US House of Representatives and a third of US Senate seats were up for grabs.
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